1. Field of the Invention
The field of the present invention is internal combustion engines of the type having a fuel injection valve disposed in the middle of an intake passage with an assist air supply means for finely dividing the fuel, an exhaust gas circulation device for circulating the exhaust gas from the exhaust passage to the intake passage, a swirl control device for producing a swirl in the combustion chamber in accordance with the operational condition of the engine, and a control means for controlling the operations of the assist air supply means, the fuel injection valve, the exhaust gas recirculation device and the swirl control device.
2. Description Of The Prior Art
An internal combustion engine which is capable of being switched between a swirl operation for a lean burn during a low load on the engine and a non-swirl operation for a burn based on a theoretical air-fuel ratio during a high load on the engine is known, for example, from Japanese Laid-open Patent Application No. 142053/85. If the ejected fuel is finely divided by assisting air in such a prior art engine, an improvement in combustibility and a reduction in specific consumption of the fuel can be achieved. Also, it is known to provide an improvement in specific consumption of the fuel and reduce NOx in the exhaust gas by the recirculation of the exhaust gas. In order to further improve the reduction in specific consumption of the fuel, a combination of the air-assisting with the recirculation of the exhaust gas is possible. However, if the recirculation of the exhaust gas is conducted irrespective of the operational condition of the engine, there is a possibility that the combustibility may be reduced. More specifically, if the recirculation of the exhaust gas is conducted during a low load operation in a lean burn condition, a deterioration of the combustibility occurs.